1. Field of the Invention
The present invention pertains to an apparatus in a fluid supply system that mixes a primary fluid flow with a secondary fluid flow, and, in particular, to a fluid mixing apparatus, delivery system, and method in which the secondary fluid flow is introduced into the primary fluid flow in such a manner so as to minimize disruption of the fluid flow profile of the primary fluid flow.
2. Description of the Related Art
It is known to provide a flow of breathing gas to a patient to treat a medical disorder. For example, ventilators, either invasive or non-invasive, are used to augment a patient""s respiratory effort or to take over that function entirely by providing a flow of breathing gas, such as air, oxygen, or an oxygen mixture, to the patient. It is also known to provide breathing gas to a patient via a pressure support device to treat other breathing disorders, such as sleep apnea syndrome. For example, it is known to use a continuous positive airway pressure (CPAP) device to supply a constant positive pressure to the patient to treat obstructive sleep apnea (OSA). It is also known to provide a positive pressure that varies with the patient""s breathing cycle or that varies with the patient""s effort to treat OSA and/or ventilate a patient.
Ventilators and pressure support devices typically include a pressure generator, e.g., a blower, piston or bellows, that generates a primary fluid flow at a pressure that is elevated above ambient pressure. A patient circuit delivers this flow of breathing gas from the pressure generator to an airway of the patient. In treating OSA, the pressure delivered to the patient""s airway xe2x80x9csplintsxe2x80x9d the airway, thereby preventing its collapse, which is a cause of OSA. A patient interface device, such as a nasal and/or oral mask, trachea tube, or nasal cannula, couples the patient circuit to the patient""s airway for delivering the positive pressure breathing gas to the patient.
When using a pressure generating system, such as a ventilator or pressure support device, to deliver a primary flow of breathing gas to a patient, it is often also desirable to provide the patient with a secondary fluid flow, such as oxygen, an oxygen mixture, therapeutic gases or a medicated gas, in addition to the primary fluid flow, which is typically air. It is conventional to introduce the secondary fluid flow into the patient conduit in which the primary fluid flow is traveling. This is often done in the ventilator or pressure support housing itself so that the introduction of the secondary fluid flow can be measured and/or controlled in the pressure generating system. FIG. 1 illustrates a portion of such a conventional fluid delivery system in which a secondary fluid flow is introduced into a primary fluid flow in a pressure generating system
As shown in FIG. 1, a conventional fluid delivery system 30 includes a first conduit 32 that carries a primary fluid flow from a source thereof (not shown), such as a pressure generator or a tank of pressurized fluid, to a patient (also not shown). Arrow 34 indicates a main direction of travel for the primary fluid flow in first conduit 32. A second conduit 36 carries a secondary fluid flow from a source thereof (not shown), such as an oxygen concentrator or tank containing the secondary fluid, to first conduit 32. Arrow 38 indicates a main direction of travel for the secondary fluid flow in second conduit 36. In this conventional system, a T-joint 40 couples second conduit 36 to first conduit 32. Due to space limitations in the ventilator/pressure support device, the T-joint is positioned very close to the other components in the fluid delivery system. Dashed lines 42, 44, and 46 illustrate where T-joint 40 couples to the fluid delivery system.
Conventional fluid delivery system 30 also includes a pressure regulation valve 48 upstream of T-joint 40. In pressure regulation valve 48, a valve member 50 moves between an open and closed position to vent fluid from first conduit 32, thereby controlling the pressure of the primary fluid flow in first conduit 32. Valve member 50 is shown in an 40 open position in FIG. 1. A flow meter 52 is coupled to first conduit 32 immediately downstream of T-joint 40. A typical flow meter measures the flow of fluid passing therethrough by measuring a pressure differential on either side of a flow element 54, which induces a pressure drop in the primary fluid flow to create this pressure differential. Typically, relatively small conduits 56 and 58 are provided on each side of flow element 54 for communicating pressures P1 and P2, respectively, on either side of the flow element to pressure sensors (not shown) so that the pressure differential can be determined. Once this pressure differential is known, the flow rate of the primary fluid flow through the flow meter can be determined. The fluid flow exiting flow meter 52 is delivered by first conduit 32 to the patient, and a patient interface device (not shown), as discussed above, couples the first conduit to the patient""s airway. It should be noted that other flow meters, pressure sensors, bacteria filters, temperature sensors, humidifiers, valves and other elements can be provided at other locations in the first and second conduit. However, due to space constraints in conventional fluid delivery systems, pressure regulation valve 48 is preferably immediately upstream of T-joint 40 and flow meter 52 is immediately downstream, i.e., adjacent, T-joint 40.
There is a significant drawback to the above-described fluid delivery system. As the secondary fluid flow enters the primary fluid flow at T-joint 40, the secondary fluid flow disrupts the fluid profile of the primary fluid flow. The fluid profile of the primary fluid flow entering flow meter 52 affects the differential pressure across flow element 54. That is, different fluid profiles for the primary fluid flow entering the flow meter can cause the flow meter to register different flow rates and, hence, flow volumes, even though the actual flow and volume of fluid through the system remains unchanged. This is due to the specific calibration of the flow meter for a particular fluid profile and/or the turbulence resulting from directing the secondary fluid flow at a 90xc2x0 angle into the primary fluid flow.
One solution for the problem caused by the disruption of the fluid profile in the primary fluid flow due to introducing the secondary fluid flow into the primary fluid flow using a conventional T-joint is to locate the flow meter several pipe diameters downstream of the T-joint. This extra distance between the T-joint and the flow meter gives the primary fluid flow time to settle so that a constant flow profile is again achieved before the fluid enters the flow meter. This solution, however, is not practical because of the limited space in conventional fluid delivery systems and the continuing demand that such systems be kept as small as possible. The extra length for the conduit undesirably increases the size of the housing.
A possible second solution for introducing the secondary fluid flow into the primary fluid flow is to change the pathway of the primary fluid flow and the secondary fluid flow so that the two mix in a homogenous fashion. However, this solution requires a relatively large amount of space for the new pathways, and, perhaps, more importantly, introduces a pressure drop in the primary fluid flow. This pressure drop is undesirable because it adversely affects the operating ability of the ventilation and/or pressure support system. For example, such systems measure flow at the patient based on the measured flow rate at a location distal from the patient and based on the known pressure drop through the patient circuit. Introducing an additional pressure drop in the fluid mixing arrangement alters the operating parameters of the ventilation and/or pressure support system. This alteration requires costly and time consuming adaptation of the ventilation and/or pressure support system to account for the additional pressure drop, or else the performance of system may be impaired or destroyed.
Accordingly, it is an object of the present invention to provide a fluid mixing apparatus for use in a fluid delivery system that avoids the shortcomings of conventional fluid delivery systems in which two fluids are mixed while minimizing the size of such a system. This object is achieved according to one embodiment of the present invention by providing a fluid mixing apparatus that includes a first conduit adapted to carry a primary fluid flow and a second conduit adapted to carry a secondary fluid flow. The second conduit is coupled to the first conduit such that the secondary fluid flow travels from a first side around at least a portion of the first conduit. An inlet port arrangement is defined in the first conduit for communicating the secondary fluid flow from the second conduit to the first conduit. The inlet port arrangement is configured and arranged such that the secondary fluid flow alters direction before entering the inlet port arrangement and such that a size of the inlet port arrangement increases as a distance around the first conduit from the first side increases. This configuration for a fluid mixing apparatus in a fluid delivery system (1) decreases the velocity of the incoming secondary fluid flow and (2) disperses the secondary fluid flow from a single stream into a plurality of smaller streams that enter the first conduit over a relatively large circumferential area of the first conduit, thereby minimizing the disruption of the fluid profile of the primary fluid flow as the secondary fluid flow is introduced into the primary fluid flow. In addition, this configurations minimizes the flow restrictions in the primary fluid flow, and, hence, the pressure drop of the primary fluid flow through the mixing apparatus that may disrupt the operation of the fluid delivery system, especially a flow meter immediately downstream of the fluid mixing apparatus.
It is yet another object of the present invention to provide a fluid delivery system that does not suffer from the disadvantages associated with conventional fluid delivery systems. This object is achieved by providing a fluid delivery system that includes a first source that provides a primary fluid flow, a second source that provides a secondary fluid flow, and a fluid mixing element. The fluid mixing element includes a first conduit coupled to the first source to carry the primary fluid flow and a second conduit coupled to the second source to carry the secondary fluid flow. The second conduit is coupled to the first conduit such that the direction of the secondary fluid flow is altered by traveling from a first side around at least a portion of the first conduit. An inlet port arrangement is provided in the first conduit to communicate the secondary fluid flow to the first conduit. The inlet port arrangement is configured and arranged such in the first conduit that a size of the inlet port arrangement increases as a distance around the first conduit from the side increases.
It is a further object of the present invention to provide a fluid delivery method that includes mixing a primary fluid flow with a secondary fluid flow that does not suffer from the disadvantages associated with conventional fluid deliver techniques. This object is achieved by providing a method that includes providing a primary fluid flow in a first conduit, providing a secondary fluid flow in a second conduit, and communicating the secondary fluid flow from the second conduit with the primary fluid flow in the first conduit so as to minimize disruption of a fluid flow profile of the primary fluid flow in the first conduit as the secondary fluid flow is introduced into the primary fluid flow in the first conduit. Minimizing disruption of the flow profile of the primary fluid flow is accomplished by providing an inlet port arrangement in the first conduit for communicating the secondary fluid flow from the second conduit to the first conduit in which the size of the inlet port arrangement increases as a distance around the first conduit from the first side increases. In addition, the direction of the secondary fluid flow is altered to reduce its velocity prior to entering the inlet port arrangement.
These and other objects, features, and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.